1. Field of the Invention
This invention relates to a camera system capable of interchanging lenses and/or an interchangeable lens.
2. Description of the Related Art
Apart from single-lens reflex cameras using silver-halide films, camera systems in which a lens and a camera body are detachably connected and in which a plurality of interchangeable lenses can be utilized are known in the field of video cameras. In lens-interchange systems, an interchangeable lens has a photographic lens, a zoom drive section, a diaphragm, a diaphragm drive mechanism and a mount portion. The mount portion of the interchangeable lens is mechanically coupled with the mating mount portion of the camera body, thereby being mounted thereon.
Also, there are well-known systems for exchanging signals representing aperture information and automatic focusing control information and the like between an interchangeable lens and the camera body. In such systems, electrical connection between signal lines of the lens and the camera body is established by connecting electric contacts of the mating mount portions or by employing an external cable or connector.
A plurality of types of lens different from each other in focal length, zoom ratio, F number and so on are provided as interchangeable lenses.
Although the conventional camera systems have satisfactory performance of establishing mechanical, electrical and optical connections between the lens and the camera body conventional camera systems entail a problem relating to the diaphragm and the mechanism for driving the same, as described below. A suitable one of various types of driving systems (e.g., a servo motor system, a pulse motor system, and an IG meter system) is selected for the diaphragm drive mechanism according to the type of lens, the F number, the zoom ratio, the image size and so on. Even in one driving system, each of the number of diaphragm blades, the mass of the same thereof, the torque of the motor, the rotational speed of the motor varies, and the control characteristics must be changed accordingly.
The diaphragm and the diaphragm drive mechanism can be designed in conformity with one standard with respect to DC operating characteristics, but, in particular, a common design of components having different dynamic characteristics is not only difficult but disadvantageous because it greatly increases the production cost and may result in failure to utilize specific features of each type of system.
In the field of video cameras, therefore, the diaphragm control characteristics or, more specifically dynamic characteristics among the same are manually controlled on the side of the camera body each time the lens is interchanged.